Even though the present invention is described below in connection with radar systems for vehicles, it is not limited to this and may be used with any radar system.
In modern vehicles, a multiplicity of electronic systems is used, for example, if they are able to support the driver in his guidance of the vehicle. Braking assistants, for instance, are able to detect preceding traffic participants and to brake and accelerate the vehicle accordingly, so that a specified minimum distance is always maintained from the preceding traffic participants. Such braking assistants are also able to initiate emergency braking, when they detect that the distance from the preceding traffic participant is becoming too small.
In order to be able to provide such assistance systems in a vehicle, it is necessary to record data about the surroundings of the respective vehicle. In the above example of a braking assistant, it is required, for instance, to record the position of a preceding traffic participant, in order to be able to calculate the distance of one's vehicle from the preceding traffic participant.
In the detection of the position of a preceding traffic participant, the azimuth angle, for example, of the preceding traffic participant is able to be recorded, starting from the driving direction of the respective vehicle. Since functionally non-relevant objects such as manhole covers or bridges also reflect radar signals, the detection of the angle of elevation permits one to distinguish between functionally relevant and non-relevant objects.
Such a detection of the azimuth angle or angle of elevation may take place, for example, by evaluation of the phases and amplitudes of the receiving antennas of a radar system.
US document US 2012/256795 A1 shows a possible antenna for such a radar system.
For a two-dimensional antenna array having phase centers Xi and yi, the following equation applies for the phase on element i:
      φ    i    =                    2        ⁢        π            λ        ⁢          (                                    x            i                    *          sin          ⁢                                          ⁢          θ          *          cos          ⁢                                          ⁢          Φ                +                              y            i                    *          sin          ⁢                                          ⁢          Φ                    )      where θ represents the azimuth angle and Φ the angle of elevation.
In a general two-dimensional antenna array, the azimuth angle and the angle of elevation have to be calculated jointly. Because of that, the calculating expenditure rises sharply. It is therefore desirable to decouple the calculation of the azimuth angle and the angle of elevation.
It is known to the Applicant that one should use an antenna as shown in FIG. 8, in order to enable a separate calculation of the azimuth angle and the angle of elevation for small angles of elevation (cos(Φ)≈1) FIG. 8 shows the positions of the receiving elements of an antenna. In this context, the four receiving elements for the calculation of the azimuth angle are situated in a horizontal plane. The two additional receiving elements for the calculation of the angle of elevation are situated in a vertical plane above the third receiving element of the horizontal plane.
However, in a separate calculation of the azimuth angle and the angle of elevation in a multi-target scenario, the angles of elevation cannot be associated with the corresponding azimuth angles.